The source of the media headlines is this article inCell Metabolism. The full article is available on free view.

The Study

The study reviewed data for 6,381 adults aged 50 and over (average age 65) using American public health data (NHANES III). The participants were followed for up to 18 years, giving 83,308 person years worth of data.

Average calorie intake was reported as 1,823 per day (which already suggests under-reporting). This was 51% carbohydrate (by calorie intake); 33% fat intake and 16% protein intake. Most of this protein intake (11 of the 16%) was reported as protein from animal sources.

Instead of dividing the people into three equal groups, the percentage of calorie intake in the form of protein was used to allocate subjects to one of three groups:

– High protein intake was categorised as more than 20% of calories from protein (1,146 people);

– Low protein intake was categorised as fewer than 10% of calories from protein (437 people).

This is interesting in itself. Normally groups are divided so that equal numbers of people fall into each group. The most common grouping used is tertiles (3 groups), quartiles (4 groups) or quintiles (5 groups). If subjects had been divided into tertiles, 2,127 people would have been in each of the 3 groups and the percentage of protein would have been the outcome – not the input (e.g. we may have found that one third of people had protein intake lower than 14% of calories; one third had protein intake between 14-18% and the final third had protein intake higher than 18%). The method used here is not wrong, but we are not comparing equal groups and this will have a difference when relative risk comes into play – as it will.

Association between protein and mortality

This is a direct quotation from the article (my emphasis): “Using Cox Proportional Hazard models, we found that high and moderate protein consumption were positively associated with diabetes-related mortality, but not associated with all-cause, CVD [cardiovascular], or cancer mortality when subjects at all the ages above 50 were considered.”

i.e. when we looked at the 6,381 over 50 year olds there was not even an association with protein intake and all-cause mortality, or CVD mortality, or cancer mortality.

There was a relationship with diabetes mortality and protein intake, but the numbers were so tiny (one death from diabetes in one group) that this was not considered important.

And that could have been the headline – “There is no association between protein intake and mortality” – but then there would be no headline.

After finding no overall association, the researchers spotted a pattern with age and split the information into participants aged 50-65 and participants over 65. They then found (direct quotation again): “Among those ages 50–65, higher protein levels were linked to significantly increased risks of all-cause and cancer mortality. In this age range, subjects in the high protein group had a 74% increase in their relative risk of all-cause mortality (HR: 1.74; 95% CI: 1.02–2.97) and were more than four times as likely to die of cancer (HR: 4.33; 95% CI: 1.96–9.56) when compared to those in the low protein group.”

This means that there was an equal and opposite result for the over 65 group. If all the participants together showed no association and one section of the group are then separated out to show a positive association, the remaining section of the group must have a negative association. That’s the law of averages. Sure enough, the 3,342 people over the age of 65 were far less likely to die from any cause if they were in the moderate or high protein intake group. Cancer mortality for the low protein group was two and a half times the cancer mortality for the high protein group.

Cardiovascular (CVD) mortality was about the same for the high protein group and the low protein group for the 50-65 year olds. CVD mortality was then much lower for the moderate protein intake group than for the low protein intake group for 50-65 year olds. For the over 65 year olds, the highest protein intake group was the best one to be in for all-cause mortality, cancer mortality and CVD mortality.

The fact that the headlines chose to claim “protein will kill you in middle age” rather than “protein will save you in old age” just highlights the nonsense and bias.

The usual errors

There are two facts that every study fails to clarify:

1) Association does not mean causation (just because we observe singing in the bath, it does not mean that being in the bath causes singing any more than singing causes being in the bath); and

2) Relative risk is a poor measure when absolute risk can be reported instead. (You can double your chance of winning the lottery by buying 2 tickets. Your relative chance is twice as high as it was before. Your absolute chance was 1 in 14 million and is now 2 in 14 million. You’re still not going to win the lottery!)

This study has absolute risk numbers and should share them. There could be 4 deaths in 1,000 people from cancer in the high protein group and 1 death from cancer in the low protein group. This meets the headline “four times as likely to die of cancer”, but it’s hugely different to having a 1 in 1,000 chance of dying vs. a 1 in 250 chance of dying – neither of which is going to lose you any sleep at night. I’ve emailed Dr Longo to ask for the raw data on death rates to see what the absolute risk is. (And remember – this is still only in the 50-65 age group and will be the other way round in the over 65s).

Protein vs animal protein

The study claims to have adjusted for protein in general vs. animal protein to conclude that animal protein is the harmful factor and not protein per se. Call me suspicious, but I always check for conflicts of interest and the lead researcher, Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.

So the study would have us believe that animal protein increases cancer mortality in people between the ages of 50 and 65, but then magically reverses this ‘causation’ at 65 such that you’d better be in the high protein group or you’ll be dropping dead like flies. This just doesn’t make sense.

I could go into a discussion of quality animal protein (meat, eggs and dairy from pasture living animals) vs. processed animal protein (fast food burgers with white buns and ketchup, mass produced chickens, low-fat sugared yoghurts) and so on, but this cannot explain why animal protein across all the people surveyed would be allegedly harmful before the age of 65 and protective thereafter. By the way – do eat quality animal produce and don’t eat processed anything (meat or otherwise), but that’s just a general health golden rule. It can’t explain this study.

Of mice, not men

The researchers turn away from John and Jane Doe to Mickey and Minnie Mouse to try to explain the results. Dr Longo is well known for his mice experiments (he was one of the chaps whom Michael Mosley interviewed when he did his Horizon programme on Intermittent Fasting).

The researchers thus did some experiments on mice. They gave some 18 week old male mice a diet with either low (4-7%) or high (18%) protein intakes. (We don’t know if either fat or carbohydrate made up the difference for the different protein intakes). They implanted melanoma cells in Mickey Mice (gave them cancer in effect) and then looked to see how the cancer progressed over the next 39 days, while the mice were fed either high or low protein intakes. Tumour incidence was reported as 100% for the high protein group and 90% for the low protein group after 25 days. The discussion that followed centered around a term you may recall from the Horizon programme – IGF-1 – Insulin-like Growth Factor.

This could have led to the headline – “Male mice given cancer cells get cancer”, but it is being used as an explanation for the observations in the human study. The hypothesis being put forward is that protein intake increases IGF-1 and that IGF-1 helps our bodies grow and it may therefore help cancer to grow. We have not even proven if protein intake determines IGF-1 in humans and therefore the hypothesis falls over at the first hurdle. The theory then suggests that IGF-1 falls with age. So are they then saying that protein over the age of 65 doesn’t impact IGF-1 and doesn’t therefore impact growth or cancer? It still just doesn’t make sense.

The final twist was that the researchers found no significant difference when they gave animal vs. plant protein to mice. So this cannot justify the headlines condemning meat and cheese. Additionally – bang goes the ProLon™ PR!

What should we take from this?

* Humans don’t need that much protein. As a rule of thumb we need approximately 1 gram of protein per 1 kilogram of body weight. Body builders and pregnant women may benefit from more, but we don’t need that much.

Having said this, protein has a substantial metabolic advantage over carbohydrate and fat and can help with weight loss as a result[i]. Hence more than 1 gram per kilogram of body weight is not a problem – so long as the intake comes from real food and not from fake shakes.

* Protein is in virtually every food provided by nature (oils and sucrose being the only two exceptions and they’re not really food). Nature provides fat/protein combinations – meat, fish, eggs, dairy products – and carbohydrate/protein combinations – grains, pulses, fruits, vegetables. Rarely do foods have fat/protein and carb in good measure (nuts and seeds being the exceptions). Why would nature put protein in everything if it were out to get us?

* This study has made an interesting observation and that’s it. It has not provided a plausible explanation. As for the smoking comparison – this is a stunt to grab headlines – not appropriate for researchers who want to be taken seriously. Smoking presents an absolute risk – provide the same numbers for my grass-grazing roast dinner if that’s what you’re claiming.

* Should you ditch meat and dairy as a result of this? Not unless you want to deprive yourself of essential fats, complete protein and invaluable quantities of vitamins and minerals. The golden rule of diet remains unchanged and that is – eat real food! This means meat, eggs and dairy from pasture living animals; fish; nuts and seeds; vegetables and fruits in season. Enjoy whole grains and starchy veg only if you are normal weight – limit these fattening foods if not. Red wine and dark chocolate and what more could a man want? Or mouse!

p.s. just had a thought a couple of hours after this was posted. Where are the vast majority of deaths going to be among the 6,381 people who were over 50 when the study started? In the 50-65 year old group or in the 65+ year old group? The latter of course. So, notwithstanding that we have no plausible mechanism, the ‘advantage’ of animal protein is thankfully in the group that will benefit most! Looking forward to the raw data…

[i] Eric Jequier, Institute of Physiology, University of Lausanne, Switzerland, found that the thermic effect of nutrients (thermogenesis) is approximately 6-8% for carbohydrate, 2-3% for fat and 25-30% for protein. I.e. approximately 6-8% of the calories consumed in the form of carbohydrate are used up in digesting the carbohydrate and turning it into fuel available to be used by the body. In contrast, 25-30% of the calories consumed in the form of protein are used up in digesting the protein and turning it into fuel available to be used by the body. (Eric Jequier, “Pathways to Obesity”, International Journal of Obesity, (2002).)

99 thoughts on “Animal protein as bad as smoking?!”

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I find the claims on proteins effect on cancer the most troubling. If you look at the data supplied in Table S1, it gives the participants history of cancer prior to the study. 11.7% of the folks in the low protein diet had a history of cancer while 7.5% in the moderate protein group and 5.0% in the high protein group. Understanding there are a ton of variables not accounted for, it would appear that high protein diet offered a protective effect against cancer for the years leading up to the study. For the actual study period, the cancer rates between the three groups were essentially the same. The only way they could claim a significant difference is if they broke down cancer deaths from 50-65 and over 65, the theory being that a low protein diet protects against cancer from 50-65 and than promotes it after the age of 65. So in summary, low protein diet appear to cause cancer until age 50, protect from 50-65, and than promotes it again after age 65. Doesn’t seem to pass the sniff test.

Good spot Pete! Also in S1 total mortality is 40.4% – 39.6% in the large moderate protein intake group (75% of participants) and 42.9% in both the tiny (6-7% participants) low protein intake group and in the still small (18% of participants) high protein intake group. Surely the headline is moderate protein intake is best for overall death rate?
Still not got the raw data – the deaths in 50-65 and 65+ will be the most interesting
Best wishes – Zoe

Paul Jaminet, co-author of “The Perfect Health Diet,” has posted his analysis of the study; he too finds it lacking in credibility; part of his analysis:

“If they wanted us to understand whether their results are trustworthy, authors would present raw data, and then a sensitivity analysis that shows how introducing each covariate individually affects the results, then showing how including combinations of two covariates affects the results, and so forth. This would help us judge how robust the results are to alternative methods of analysis.

“Of course, authors do not do this. Instead, they ask us to trust the analysis they have chosen to present – which is only one of billions they could have done. (This study adjusted for 13 covariates. The NHANES survey may have gathered data on, say, 40 variables. There are 40 choose 13, or 12 billion, possible multivariate regression analyses that could be performed using 13 covariates on this data set. Each of the 12 billion analyses would generate different outcomes.)”

what Weston Price (with or without the foundation) has to offer to us is that limited observations lead to ecological fallacies which leads to pseudoscience (the same applies for vegan nonsense, e.g. “The China Study”).

Hi David – I’m not sure what you mean. There is no stance to be had on “essential fats” – just facts. Essential in nutrition means it’s essential that we consume the substance – the body can’t make it. Without essential fats (omega-3 and omega-6) we die, so we need to consume them. Fortunately nature puts them in most foods – all animal foods (meat, fish, eggs, dairy) and some plant foods – the ones that contain fat (avocados, olives, coconuts, nuts, seeds etc).
Best wishes – Zoe

Another great analysis! I found another on examine.com, but I like Zoe’s better. I’ve read a lot of studies over the last few years and have tried to hone my bullshit detector, but I can never ferret out the salient details like Zoe.

Well, excellent article and so many good comments that there isn’t much I can add to the discussion. Except that Weston Price noticed that the healthiest groups of people he encountered ate more animal protein (and quite a bit more animal fat!) than the average Westerner. It’s interesting to note that the theory of many explorers at that time was that hunter gatherers and other traditional groups didn’t get cancer precisely *because* they ate meat! They observed that American Indians, Africans, Inuit, and other groups were free from the diseases of civilization (including cancer), and the theory was that it was actually the meat that protected them (as opposed to replacing animal protein with other things, presumably carbs). Someone wrote a book about the high meat/lack of cancer connection; unfortunately, I can’t remember the name of this person, as I’d like to read the book! Funny though, how times have changed……
In any case, it does seem inane that animal protein would kill us at a certain age (a very strong statement, which in itself makes me suspicious)- but on our 65th birthday we can now dance with glee and eat all the animal protein we want to because the so-called negative effect has reversed itself and turned positive. This just defies logic!

“Without consistent recordings of IGF-1 levels over the years and without strict “ward” environments it is not possible to invoke a high protein/ IGF-1 / cancer link.”

Of course it’s possible, just not with enough strength to challenge long, well-conducted trials. As for metabolic ward studies, their strength lies elsewhere since due to restrictions in n and length they cannot provide conclusive evidence on whether a given issue is of that much relevance in the real world and/or whether lifestyle interventions etc. etc. can address it or not.

“The fact that this “study” has been reported worldwide is sad but then it fits right into the HCLF dietary pattern lauded by the pundits.”

I suppose everything which YOU don’t want to hear fits right into that. HCLF diets can be low, moderate or high in protein, just like LCHF diets.

“Protein is helpful to 65 year olds but detrimental to those who are 55? Highly unlikely. This screams ‘confounding factors’, not to mention ‘lying on the survey’!”

See the “Discussion” part in the study. It’s not actually a miracle or even new information that things change when you get olders. Higher protein intake can reduce excessive weight loss due to the loss of muscle mass (which is very much a problem among the elderly) and also excessive drop in IFG-1 levels.

Thank you so much for your analysis. Researchers throw around fancy, sciency-sounding words, and get people to believe that the analysis they’ve provided is high quality, when in reality, it’s problematic.

I am just coming to realize that almost everything I’ve learned about good nutrition in my life is really flawed, and the notion that “a calorie is a calorie” is woefully inadequate for describing macronutrients…especially as I begin to understand more about cellular respiration, and the interplay between the liver and cells.

Do you think the term “protein” is too simplistic of a term, given the amount and impact of different amino acids?

The authors stacked the deck in that study. First, they added methionine to the typically caseine-only protein in these rat chows, knowing full well that methionine has been shown to decrease longevity in rats. So, the rats who got the most protein also got the most methionine. Predictably, they died sooner. Secondly, the fat used in this study is not saturated or even trans, it is entirely soybean oil. No wonder those rats who ingested the most fat died earlier (and likely with moobs).

Here in Australia we were bombarded with headlines about the risks of consuming a high protein diet due to another study conducted by the University of Sydney, published in the same ‘Cell Metabolism’ Journal as the one you have covered.

This study claims to determine that a high carb, low protein diet is associated with a longer life span. I was wondering if you saw this and if so, what are your thoughts?

“After finding no overall association, the researchers spotted a pattern with age and split the information into participants aged 50-65 and participants over 65. They then found (direct quotation again): “Among those ages 50–65, higher protein levels were linked to significantly increased risks… etc”

Great analysis, Zoe!

Protein is helpful to 65 year olds but detrimental to those who are 55? Highly unlikely. This screams ‘confounding factors’, not to mention ‘lying on the survey’!

Thanks Zoe for doing what we all knew you would – uncover the real story. Fantastic job and we can’t thank you enough! And thanks to FrankG for the additional info on the authors.
BTW, protein shakes are not “invariably soy based”. Bodybuilders and strength athletes have been aware of the effects of soy for many years and the market responded a long time ago – most protein formulas targeting male athletes don’t have any soy.

“Call me suspicious, but I always check for conflicts of interest and the lead researcher, Dr Longo, has declared interests in (actually, he’s the founder of) L-Nutra – a company that makes ProLon™ – an entirely plant based meal replacement product.”

In case you had missed this (unlikely) it was not just Valter D. Longo but three others of the authors (Sebastian Brandhorst, Priya Balasubramanian and Luigi Fontana) working for L-Nutra…

This “study” invokes IGF-1 as the driver behind the cancer outcomes. Without consistent recordings of IGF-1 levels over the years and without strict “ward” environments it is not possible to invoke a high protein/ IGF-1 / cancer link. The assumptions are, to put it bluntly, as valid as those in a Hans Christian Andersen story. These folks have invoked a “mice and men” link that is pure homage to fairy tales.

Worse, none of the protein percentages amount to anything like “high!” Indeed, the data indicate that a low protein intake is the problem, except that it is not possible to know with any assurance what the real protein intake was given the method of self-reporting. A high protein intake would be 2gm/kg body weight but this is far from what they understood to be high/low protein intake. In fact, 2 gm/kg is “optimal” for active people on high energy output days. For a 70 kg person this is about 700 gm of MEAT per day.

The fact that this “study” has been reported worldwide is sad but then it fits right into the HCLF dietary pattern lauded by the pundits.

I agree with your assertion that protein supplemts aren’t ‘food’, but for anyone trying to build lean body mass, they are certainly beneficial. Studies show that for optimal muscle protein synthesis you must ingest a relatively high (20-30g) amount of protein at once, and repeat this every few hours. The fact is, it isn’t easy, or cheap, to consume optimal amounts of protein for maximal MPS, through strictly whole, real foods.

When I read the summary of this in the Washington Post, it sounded like “damned lies and statistics” from the get-go and I wondered who had taken the study apart first; then I thought to look for for the analysis here — thanks for this, Zoe!

However, one thing I wish were always highlighted when discussing this sort of study is the validity of the study data itself. Almost all of these epidemiological studies rely on food frequency questionnaires that ask respondents to remember what they ate weeks, months, and in some cases, YEARS ago. Everyone should read Chris Masterjohn’s classic blog post in which (in the second half of the post) he discusses how the huge Nurses’ Health Study had a subgroup of nurses actually weigh and measure everything they ate for a week 4 times a year, and then reply to a food frequency questionnaire. Comparison between the weighed and measured data and the questionnaire data showed that the nurses hugely overestimated the vegetable servings they ate and hugely underestimated the amount of hamburgers they ate, among other things; see http://blog.cholesterol-and-health.com/2010/09/new-study-shows-that-lying-about-your.html

Which raises the question of why researchers even bother to do these big “what did you eat and how sick did you get” kind of studies; they must have error margins big enough to to drive a truck — sorry, a lorry — through, even if the researchers aren’t up to some shady manipulation of the numbers, as you show that they were here.

By the way, to the Washington Post’s credit, they at least included this: “Marion Nestle, a nutrition expert and public-health professor at New York University, said the findings raise as many questions as they answer. She said they don’t amount to a convincing argument that too much protein consumption in middle age is directly linked to health problems later in life, while more protein in old age is protective. … ‘I’m also puzzled by the idea that there is a significant difference between the effects of protein from animal and vegetable sources,’ Nestle said. ‘Protein is not, and never has been, an issue in American diets, and the data presented in this study do not convince me to think otherwise.'” I wonder if the UK papers were as conscientious in giving space to a contrary viewpoint?

Q: On what planet does a human diet deriving 20% of total energy from protein = a “high-protein” diet?

A: On Planet Wacko, where—
Consuming more than 1/2 drink/day makes one a “heavy drinker”…
Having more than 2 sexual partners in a lifetime makes one “promiscuous”…
Walking more than 400 meters/day makes one “highly active”…

It’s also worth noting that of participants with a ‘history of diabetes’, 28% were in the ‘high’ categories, versus 2% in the ‘low’. Of those who had changed their diets, 23% were now in the ‘high’ group vs 4% in the ‘low’. It would not be surprising if those with diabetes consumed a higher percentage of their intake from protein due to the constraints of attempting to limit GI foods and refined carbohydrates. This could imply that people with a history of diabetes may have a disproportionate representation

Similarly, of those who had attempted to lose weight 21% were in the ‘high’ vs 7% in ‘low’. Therefore it is possible that yo-yo dieters or those who are encouraged to lose weight due to a history of weight related disease in their family (such as diabetes) are more likely to be present in the ‘high’ catergory rather than the ‘low’.

Therefore if more people with a personal history of diabetes (as is reported) or if the above analysis on the probability of family history of diabetes holds true, we really shouldn’t be all the surprised that those people are more likely to subsequently die of diabetes. The actually death rates from any cause where also identical for both groups (42.9%) so ultimately something got them within the time frame, it’s a shame we don’t have the data into ages of death.

A final interesting point is that these were self-reported and done so to a dietician. We now know the prevalence of under reporting of food intake, particularly for ‘unhealthy’ things. So it seems possible that the unreported food is more likely to be in the form of high carb/fat foods (larger bowls of cereal, handfuls of crisps, slightly more alcohol) rather than the form of animal protein. People are unlikely to forget that had chicken for dinner or to be embarrassed to report it to a dietician. This would obviously particularly skew the report, slightly (though protein calories were still ~1/3 greater than average). It’s particularly interesting to note that the ‘high protein’ group reported the lowest total calorie intake of <1,600kcal, whereas the 'low protein' group reported the highest ~2,000kcal and 15% also admitted to this being less than they usual ate. Seems to tally slightly more honestly with the current obesity rates…

Fantastic analysis Zoe.
A couple of additional things struck me about the papers:
1) the incredible number of contributing authors. This sort of massing of scientists is not normal – it is something usually seen on manifestos. It is very unlikely that this many people agreed with the conclusions on the thin science grounds, which makes it likely that they have gathered for some other reason – a common belief system (such as veganism), or an interest in promoting protein restriction as cancer therapy. Which takes us to:
2) The mouse paper. Protein restriction is a legitimate cancer therapy (at least in mice). Of course what inhibits an existing cancer may not be what would have prevented it from starting in the first place (radiation both causes and inhibits cancer). But look at what (I’m told, correct this if wrong or incomplete) these mice ate: the protein (the variable item) was casein, plus DL-methionine. D-methionine is a rare amino acid, non-essential, not usually toxic to mice, but, if the mouse has cancer, who knows? It’s in every experimental diet, for some reason. Certainly not something recommended for human consumption. The high-animal protein mice ate more of this. Soy oil, grain starch, sugar. Added vitamins and minerals. Colouring.
Also, where was the age difference in the mice? All that study shows is that protein restriction is a cancer therapy (one of many, humans might prefer ketosis, radiation, chemotherapy) but we knew that already.
Usually cancer is more prevalent in ageing populations. It’s nice to think that animal protein reverses this trend, but I wonder how many other nutrients were separated in the data. Refined starch, sugar, and polyunsaturated oil are all things that should have been adjusted for separately. We’ll see if they were.

As you note, there’s all sorts of confounding factors. One is meat-based proteins tend to come with animal-based fats, and there’s excellent reason to believe animal fats may be an issue, especially given the way our animal products are prepared.

The whole think just doesn’t add up and when you said he owns that company then it becomes clear. Sadly vegetarians will be all over this and I’ll have to listen to people telling me how I’m going to die from my meat consumption because they only read the headline.

Tell that to jon Andersen who I blogged about at strengthandvirility.com, he lives off nothing but grass fed beef. He looks a hell of a lot better than any vegetarians I know.

….. I’m not trying to bash veggies but they seem to be obsessed with converting the planet to their way of eating. At least there will be more meat available for me. :)

While I certainly agree with your assessment of the reporting and the headlines, I do think care should be taken not to conflate that with the study itself. The study does not mention the risk of smoking at all. The quote in the articles does come from Dr. Longo, however, and it first appears in the USC press release about the study.

Frankly, this press release is horrendous and it should probably be the target of your attack. As for the meat and cheese statements, those also comes primarily from the press release.

I still suspect that the animal vs plant protein conclusion will hold up in an independent analysis of the data– at least well enough to merit further research. While this study does not distinguish between high-and low quality protein sources, it is worth noting that it never claims to. A comparison of the effects of high and low-quality plant and animal protein sources is out of the scope of the study (and probably not possible with the existing data).

While the conclusions in the study are not the same as those in the press release and subsequent articles, I have a harder time disregarding the study’s conclusions based on Dr. Longo’s disclosure of interest than you do. I’d be very interested to see somebody else run the numbers, as I’m not qualified to do so myself. I know enough to know that I’m out of my depth here :)

Hi MB – good point on the distinction between the press release and the study. The press release has become the gateway to the media unfortunately and researcher ethics are being compromised for researcher egos in this respect. The only thing better than a published study is a study that hits the headlines and Longo’s reference to smoking achieved that – completely inappropriately from what I’ve seen in the study.

I also want to run the numbers – I’ve asked for the raw data on deaths and subjects by condition, by age, by protein intake. As per my p.s. – I suspect the majority of deaths are in the over 65s – where higher protein intake is associated with lower mortality and the smaller number of deaths in the 50-65 group may explain some of the large confidence intervals and relative risks.

Hey Zoe, in the conclusion section of this analysis, you state that extra protein isn’t bad, as long as it comes from natural foods and not shakes. What’s wrong with shakes? Is the protein of lower quality or something? Or is it that the shakes come full with a variety of other stuff that aren’t as good for you?

Thanks Zoe for your most sensible article, as always.
As a 66 year old, I have finally returned to the sensible diet of my 1950s childhood, and wish I had never been influenced by the barmy ‘researchers’ during the intervening years.
So….moderation in all things.
Quality animal proteins, known as 1st class in days gone by.
Mixed fats from all natural sources…..sats, MCTs, and a smattering of PUFAs from seeds and a few nuts.
But, admittedly, less carbs than I would have consumed….because even fresh fruits and grains have been so modified, that they are no longer a reliable source of anything!
But, I now enjoy quality chocolate, which was not readably available then, plus a glass of red wine, which I have come to late in life.
It has taken me a year to sort through the dreadful mess that our food industry has got us into….but being retired, I have the time, and inclination, to get to grips with it all…much to the advantage of my health status.

Isn`t research wonderful. I follow ( since 2007 ) a lo-carb regime due to t2 and at the time being very close to 20st. I lost a shed load of weight and all of a sudden felt and was a whole lot better. At every check-up I got a well done because the numbers were pretty good. What the nurse/GP wasn’t interested in was my diet. Oh well if it works for you!!.
With the current hoo hah about the NHS flogging patient data in my particular case it would be something of a non runner because all they will get is medication history but nothing about what I eat. The fact that I showed improvement with a condition that is generally thought to deteriorate would be attributed to the wonder of drugs not life style or diet.

All of this is easily explained by digestible/metabolizable energy. The high animal protein diets will have more available calories versus plant protein only, or a plant/animal combination, due to the ease with which we digest animal products and the fat content. More calories mean more likely to be overweight, which means more likely to be diabetic, and on…..
This is probably why the elderly group (> 65) did well with higher protein. They eat less (total volume) than younger people, consume fewer calories, and so, a protein-dense diet is beneficial for them.
So, the protein is beneficial, and the excess calories is the real problem.
I hate to say it, but calories in, calories out……